The present invention relates generally to endoscopes and, more particularly, to mechanisms in endoscopes for controlling the curvature of a bendable portion defined by the front end region of the flexible tubular member of the endoscope.
In endoscopes of the type which are adapted to be inserted into a body cavity for purposes such as the diagnosis, treatment, and/or operation of a digestive organ or the like, the bendable portion constituting the free front end region of the flexible tubular member which has been inserted into the body cavity must be bent in a controlled manner through external manipulation of components of the endoscope. To this end, various mechanisms for controlling the curvature of the bendable portion of the endoscope have been proposed. Many of the curvature control mechanisms utilize an arrangement wherein a plurality of control wires extend parallel to one another from the forward bendable portion through the flexible tubular member or intermediate portion of the endoscope to a manipulator unit to which the flexible tubular member is attached. The application of a pulling or tension force on one of the control wires results in a tension-relief of another control wire so that a desired curvature of the bendable portion of the endoscope is achieved.
Various improvements in curvature control mechanisms used in connection with the arrangement described above have been suggested. Many of these suggested improvements are directed to solving the problem of the presence of excessive slackness in the control wire which is tension-relieved. In other words, improvements have been suggested whereby the control wire which is moved in the direction away from the tension-loaded side will be provided with a required degree of slackness with any excessive slackness being effectively eliminated so that the tension-relieved wire will not become entangled or irregularly stagnated so that a desired curvature control is reliably achieved in a relatively smooth manner.
In an arrangement wherein curvature control is achieved by pulling one of a plurality of wires while another wire is tension-relieved, guide holes are generally provided through which the control wires extend both in the flexible tubular member as well as in the bendable front end portion thereof. These guide holes have diameters which are slightly larger than the outer diameter of each control wire passing therethrough in order to assure a desired smoothness in the manipulation of the curvature control mechanism. In consequence, as understood by those skilled in the art, when the bendable front end portion is bent, the control wire on the tension-loaded side is slidably moved or drawn through a series of guide holes along the sections of their inner walls which are remote from the longitudinal axis of the bendable front end portion. On the other hand, the control wire on the tension-relieved side is slidably moved through its series of guide holes along sections of their inner walls which are nearer to the longitudinal axis of the bendable portion. As a result, the length of the control wire on the tension-relieved side which is actually delivered forwards during the bending operation is shorter than the length of the wire on the tension-loaded side which is actually taken up, and this necessitates an excessive slack. Moreover, the control wire on the tension-loaded side will often stretch or extend along itself and, in such case, the wire will be pulled with an excess of this extension or stretched amount to obtain the desired curvature. Consequently, the length of the control wire on the tension-relieved side to be delivered forwards during the bending operation will be yet even shorter than the length to be pulled and the wire on the tension-relieved side will have an even further excessive slackness which may result in the wire being flexed, bent or forcibly compressed within the guide holes causing entanglement, stagnation or untwisting. This in turn may cause a serious obstacle to the smooth manipulation of the mechanism. Such circumstances which occasionally occur in prior art apparatus have sometimes caused fatal accidents, such as when a control wire breaks since such an accidental breakage of a control wire in an endoscope which had already been inserted into the body cavity with the forward bendable portion thereof already in a curved condition will render it difficult to remove the endoscope from the body cavity. It is clear that such a circumstance is extremely dangerous in the use of endoscopes in diagnosis, treatment or operation. Thus, it is already known that the slackness inevitably generated in the control wire on the tension-relieved side, which slackness is not only unnecessary but also detrimental in the operation of the endoscope, must be absorbed or eliminated in order to overcome the problems discussed above and to this end various suggestions have been proposed. However, conventional prior art mechanisms incorporating such suggestions have not entirely solved the problem since such suggestions involve not only merits but also are encumbered with certain disadvantages.
For example, an arrangement is disclosed in Japanese Utility Model Disclosure Gazette No. 1974-80087 where each control wire is provided with a coil spring along a portion of the associated channel through which the wire is guided so that the wire on the tension-loaded side will be subjected to a tension by such a coil while an excessive slackness in the wire on the tension-relieved side will be absorbed by a self-compression of the associated coil spring. However, in this arrangement, a control wire must be continuously biased under tension of the coil spring to absorb the slackness due to excessive tension-relief and it has been found difficult to maintain the biasing characteristic of the coil spring in view of the fact that the spring unavoidably becomes fatigued in operation. When a coil spring having a greater biasing effect is utilized in an attempt to compensate for this problem, the heavier loads thereby presented prevents a smooth manipulation of the mechanism. On the other hand, when a coil spring having a lower biasing effect is utilized, the wire on the tension-loaded side cannot be adequately pulled or drawn while the excessive slackness in the wire on the tension-relieved side cannot be satisfactorily absorbed or eliminated.
In another proposed arrangement disclosed in Japanese Patent Disclosure Gazettes Nos. 1977-144177 and 1977-144178, a separate elastic member is provided which is adapted to maintain the control wire on the tension-relieved side in a tensioned condition.
Many other suggestions have been made in addition to those discussed above. Thus, Japanese Patent Disclosure Gazette No. 1978-105079, Japanese Utility Model Disclosure Gazettes Nos. 1978-116180 and 1977-158586, and Japanese Utility Model Publication No. 1976-43030 disclose an arrangement wherein the free end of each control wire is provided with a projection and a corresponding member provided which is adapted to be engaged by the projection so that the wire is tension-loaded by such engagement when the wire is pulled on the tension-loaded side while, on the tension-relieved side, a slackness is eliminated as the member is freely disengaged from the corresponding projection.
In another proposed arrangement, the control wire is pulled through the rotation of a rotary pulley which is formed in a manner such that its effective radius varies as the pulley is rotated (see Japanese Utility Model Disclosure Gazette No. 1975-49283).
Still further, an arrangement is disclosed in Japanese Utility Model Disclosure Gazette No. 1979-108590 wherein a take-up pulley and a rewinding pulley are rotated by a common manipulating knob. Predetermined play or tolerances are provided in opposite directions between a rotation transmitting shaft so that the two pulleys are rotated by that rotation transmitting shaft in a manner such that, on the rewinding side, the rewinding pulley will have an idle rotation as a spring on the rewinding side is compressed.
None of the prior art arrangements which have been suggested heretofore have proven to be entirely satisfactory. Thus, the prior art suggestions have disadvantages and difficulties such as being relatively mechanically complicated and requiring relatively bulky dimensions resulting from the necessity of incorporating a plurality of separate components into the mechanism.